JP2007305396A - Electrode for secondary battery and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for a secondary battery having high short circuit resistance and a high current collecting property by making bear the current collecting property to the metal rich layer having higher metal density than other part of a three-dimensional metallic porous body and making arrangement of the metal rich layer fair. <P>SOLUTION: The electrode for the secondary battery is formed by filling an active material in pores of the three-dimensional metallic porous body, and the metal rich layer having higher metal density than other part of the three-dimensional metallic porous body is formed in a portion other than a surface layer part in the thickness direction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrode for a secondary battery used for an alkaline storage battery and the like, and more particularly to a technique for solving a structural problem and suppressing a short circuit during winding.

  Secondary batteries, especially alkaline storage batteries, have a high capacity against overcharge and irregular patterns of charge and discharge while having a constant capacity density, so they are segregated from non-aqueous electrolyte secondary batteries mainly for tough use applications. Is progressing.

  The alkaline storage battery electrode is roughly classified into a paste type electrode and a sintered type electrode. In recent years, from the viewpoint of increasing capacity, a paste-type electrode in which a paste mainly composed of an active material is filled in a void of a three-dimensional metal porous body such as a sponge-like metal porous body or a nickel fiber nonwoven fabric is used as a positive electrode of an alkaline storage battery. It is utilized.

  These three-dimensional metal porous bodies have a porosity (ratio of void volume occupying the total volume) of about 95%, and the pore diameter of the voids reaches up to several hundred μm. Is possible. However, in order to obtain a high-capacity paste-type electrode, when the porosity is randomly increased and the paste is filled more, the proportion of the three-dimensional porous metal in the portion filled with the paste becomes too low, and the current collector And the discharge characteristics of the secondary battery are likely to deteriorate.

For these problems, the structure of the three-dimensional metal porous body is devised as in Patent Document 1, or the paste filling method is devised as in Patent Document 2, so that the thickness direction of the three-dimensional metal porous body is improved. A technique has been proposed in which only one side is filled with an active material, and an electrode structure that collects current on the other side that is not filled with an active material is realized to enhance the discharge characteristics of the secondary battery.
JP 2000-208144 A Japanese Patent No. 2976863

  By the way, when the paste type electrode using a three-dimensional metal porous body is wound together with a counter electrode and a separator in a spiral shape and accommodated in a cylindrical can, cracks are generally likely to occur near a wound core having a small curvature. The electrode produced by using the techniques of Patent Documents 1 and 2 has unevenly distributed portions (hereinafter referred to as metal-rich layers) where the abundance ratio of the metal is high only on one side of the surface. Since the metal rich layer itself has a degree of freedom with respect to stress as compared with the portion filled with the active material, it has a high resistance to bending, and cracks due to winding are unlikely to occur. However, the metal skeleton is irregular and discontinuous on the surface of the three-dimensional porous metal body. Therefore, during winding, the discontinuous metal skeleton of the metal rich layer protrudes from the electrode surface, breaks the separator, and an internal short circuit easily occurs due to contact with the counter electrode. In particular, since the end face of the electrode has many discontinuous metal skeletons by cutting, an internal short circuit is more likely to occur.

  This invention is for solving the said subject, and provides the electrode for secondary batteries with both high short circuit resistance and high current collection property by optimizing arrangement | positioning of the metal rich layer which bears current collection property. For the purpose.

Based on the above problems, the electrode for a secondary battery of the present invention is obtained by filling the voids of the three-dimensional metal porous body with an active material, and the metal of the three-dimensional metal porous body at a location excluding the surface layer portion in the thickness direction. It is characterized in that a metal rich layer having a density higher than other portions is provided.

  Further, as a manufacturing method for obtaining the above-described secondary battery electrode, the secondary battery electrode manufacturing method of the present invention is mainly composed of an active material in the voids while running a strip-shaped three-dimensional porous metal body. An electrode precursor that is filled with paste and discharges paste from a pair of paste discharge nozzles arranged on both sides of the three-dimensional metal porous body so that an unfilled portion remains inside the three-dimensional metal porous body. The method includes a first step for manufacturing the electrode precursor, a second step for drying the electrode precursor, and a third step for rolling the electrode precursor.

  Since the metal rich layer itself has a degree of freedom with respect to stress as compared with the portion filled with the active material, it has a high resistance to bending. However, when there is a metal-rich layer only in the surface layer part of the electrode as in Patent Documents 1 and 2, the discontinuous metal skeleton of the metal-rich layer protrudes from the electrode surface by winding and breaks the separator and contacts the counter electrode Internal short circuit is likely to occur. However, since this metal rich layer is not located in the surface layer part of an electrode, this invention can clear the subject which the electrodes of patent documents 1-2 have.

  According to the present invention, the metal-rich layer responsible for current collection can be appropriately disposed. Therefore, an electrode for a secondary battery having both high short-circuit resistance and current collection and a high-performance secondary battery are provided. Can be provided.

  The best mode for carrying out the present invention will be described in detail with reference to the drawings.

  In the first invention, the voids of the three-dimensional metal porous body are filled with an active material, and the metal density of the three-dimensional metal porous body is higher than that of other portions in the portion excluding the surface layer portion in the thickness direction. The present invention relates to an electrode for a secondary battery, characterized in that a layer is provided.

  FIG. 1 is a schematic cross-sectional view showing a secondary battery electrode of the first invention. While the electrode is formed by filling the voids of the three-dimensional porous body 1 with the active material 2, the metal rich layer 3 in which the metal density of the three-dimensional metal porous body 1 is higher than that of the other portions in the portion excluding the surface layer portion. Is provided. Although this metal rich layer exists also in patent documents 1-2 as shown in FIG. 2, since the metal rich layer 3 is not located in the surface layer part of an electrode in this invention, the subject which the electrodes of patent documents 1-2 have Can be cleared.

  As the first effect, since the metal rich layer 3 is not located in the surface layer portion of the electrode, an internal short circuit caused by a discontinuous metal skeleton of the metal rich layer protruding from the electrode surface during winding as in Patent Documents 1-2. Can be eliminated. As a second effect, the portion filled with the active material 2 has a lower resistance to bending than the metal rich layer 3 and is likely to crack. However, since this crack does not grow beyond the metal rich layer 3, It can improve the resistance to bending. By these first and second effects, an electrode with high short-circuit resistance can be realized.

  Here, as the three-dimensional porous body 1, it is possible to use a sponge-like metal porous body or a fiber nonwoven fabric made of nickel or nickel-coated iron as a raw material. As the active material 2, nickel hydroxide powder can be used for a positive electrode for an alkaline storage battery, and hydrogen storage alloy powder can be used for a negative electrode for an alkaline storage battery. When nickel hydroxide powder is used as the active material 2, a conductive agent such as cobalt hydroxide or metallic cobalt, a binder such as polytetrafluoroethylene (hereinafter abbreviated as PTFE), or carboxymethyl cellulose (hereinafter abbreviated as CMC). A thickener such as can be used together.

  The second invention is characterized in that, in the first invention, the ratio of the thickness of the metal rich layer 3 to the thickness of the electrode is 5 to 15%. When the ratio of the thickness of the metal rich layer 3 to the thickness of the electrode is less than 5%, it is difficult to give the metal rich layer 3 the first and second effects described above. On the other hand, in order to maintain the battery capacity, if the weight ratio of the metal rich layer 3 is made to exceed 15% while keeping the weight per unit area (metal weight per unit area) constant, the first three-dimensional metal Since it is necessary to make the porous body 1 thick, the metal skeleton in the portion filled with the active material 2 becomes thin, and a crack is generated at the time of winding, so that the probability of inducing an internal short circuit is increased.

  According to a third invention, in the first invention, the position of the metal rich layer 3 is periodically changed in the thickness direction of the electrode. FIG. 3 is a schematic cross-sectional view showing a secondary battery electrode of the third invention. The position of the metal rich layer 3 periodically changes in the thickness direction of the electrode. Since the bellows structure is obtained by periodically changing the metal rich layer 3, stress due to the metal rich layer 3 being pulled at the time of winding is relieved, which is preferable. In addition, when the electrode of the third invention is wound, cracks are likely to occur at the place where the distance from the surface layer to the metal rich layer 3 on the outside at the time of winding is the largest, but the interval is relatively large, Compared to the first invention in which uniform shallow cracks are likely to occur, the number of cracks can be reduced, and the short-circuit resistance can be improved.

  According to a fourth aspect of the invention, while the strip-shaped three-dimensional metal porous body is run, the voids are filled with a paste mainly composed of an active material so that an unfilled portion remains inside the three-dimensional metal porous body. A first step of producing an electrode precursor by discharging paste from a pair of paste discharge nozzles disposed on both surfaces of the three-dimensional metal porous body, a second step of drying the electrode precursor, and an electrode precursor The manufacturing method of the electrode for secondary batteries characterized by including the 3rd process of rolling a body.

  FIG. 4 is a schematic cross-sectional view showing a first step in the method for producing a secondary battery electrode of the fourth invention. By disposing a pair of paste discharge nozzles 4 on both sides of the band-shaped three-dimensional metal porous body 1 running from the lower side to the upper side in FIG. 4, the paste 5 mainly composed of the active material 2 is discharged. The electrode precursor 6 is produced. Here, by adjusting the discharge amount of the paste 5 so that an unfilled portion of the paste 5 remains inside the three-dimensional metal porous body 1, the electrode precursor 6 that has undergone the second to third steps (not shown) is obtained. It can be set as the electrode for secondary batteries shown in 1st invention.

  According to a fifth invention, in the fourth invention, while the total amount of paste 5 discharged from the pair of paste discharge nozzles 4 in the first step is made substantially constant, one paste discharge nozzle 4 and the other paste discharge nozzle 4 The discharge amount is periodically changed. By adopting such a method, the electrode precursor 6 having undergone the second to third steps can be used as the secondary battery electrode shown in the third invention.

  The present invention will be further described in detail by the following examples.

Example 1
A pair of paste discharge nozzles 4 are arranged on both sides of a three-dimensional metal porous body 1 (thickness 2.0 mm, basis weight 700 g / cm ³ ) traveled at 5 m / min, and nickel hydroxide powder as an active material 2 (Average particle size 10 μm) 10 parts by weight of cobalt hydroxide, 0.5 parts by weight of PTFE, 0.3 parts by weight of CMC and an appropriate amount of water (solid content ratio 70%) to 100 parts by weight are constant with a pump The liquid was discharged while applying a pressure of 0.5 mm from the surface layer of the three-dimensional metal porous body 1. The electrode precursor 6 is dried and then rolled to a thickness of 0.68 mm, and the metal rich layer 3 (thickness: 0.10 mm, thickness ratio to electrode thickness: 15 at the center in the thickness direction is large). %). This was processed into a length of 35 mm and a width of 250 mm, and a lead plate was attached to form a positive electrode. This is Example 1.

(Example 2)
Compared to Example 1, the thickness of the three-dimensional metal porous body 1 was 1.2 mm, and the electrode precursor 6 was dried and then rolled to a thickness of 0.61 mm. A positive electrode was produced in the same manner as in Example 1 except that the thickness was 03 mm (ratio of thickness to electrode thickness: 5%). This is Example 2.

(Example 3)
Compared to Example 1, the total amount of the paste 5 discharged from the pair of paste discharge nozzles 4 is kept constant by 1.0 mm in the thickness direction of the three-dimensional metal porous body 1, while one paste discharge nozzle 4 and the other paste discharge nozzle 4. The discharge amount of the paste 5 was periodically changed within the range of 0.30 to 0.70 mm when the three-dimensional porous metal body 1 traveled 10 mm. A positive electrode produced in the same manner as in Example 1 except for this is referred to as Example 2. Note that the ratio of the thickness of the metal rich layer 3 to the thickness of the electrode was 15% as in Example 1.

Example 4
In contrast to Example 1, the thickness of the three-dimensional porous metal body 1 is 3.5 mm, and the electrode precursor 6 is dried and then rolled to a thickness of 0.73 mm. A positive electrode similar to that of Example 1 was prepared except that the thickness was 15 mm (ratio of thickness to electrode thickness: 20%). This is Example 4.

(Example 5)
In contrast to Example 1, the thickness of the three-dimensional metal porous body 1 was 1.1 mm, and the electrode precursor 6 was dried and then rolled to a thickness of 0.60 mm. A positive electrode was produced in the same manner as in Example 1 except that the thickness was 02 mm (ratio of thickness to electrode thickness: 3%). This is Example 5.

(Comparative Example 1)
In contrast to Example 1, the thickness of the three-dimensional metal porous body 1 was 1.0 mm, and the electrode precursor 6 was dried and then rolled to a thickness of 0.58 mm, so that the metal rich layer 3 was not formed. Except for this, a positive electrode similar to that of Example 1 was produced. This is referred to as Comparative Example 1.

(Comparative Example 2)
For Example 2, the paste 5 was discharged from only one paste discharge nozzle 4 and filled to a depth of 1.0 mm from the surface layer of the three-dimensional metal porous body 1 to obtain an electrode precursor 6, which was dried. Later, the metal rich layer 3 (thickness 0.03 mm, ratio of thickness to electrode thickness 5%) was formed only on one surface layer portion by rolling to a thickness of 0.61 mm. A positive electrode produced in the same manner as in Example 2 except for this is referred to as Comparative Example 2.

The obtained positive electrode of each example and comparative example was subjected to a negative electrode (thickness 0.5 mm, length 35 mm, width 300 mm, Mm is a mixture of light rare earths) and a hydrophilic treatment using a known MmNi ₅ type hydrogen storage alloy. The electrode group was configured by winding in a spiral manner through the polypropylene nonwoven fabric separator (thickness 0.15 mm, length 39 mm, width 550 mm).

The crack generation state of this electrode group was calculated as a percentage by measuring the maximum value of the crack depth in the thickness direction of the positive electrode on the bottom surface of the cylindrical electrode group. In addition, 1000 electrode groups were prepared, and if the resistance when a voltage of 150 V was applied was 2 kΩ or more, an insulating evaluation was made to pass, and the ratio of the electrode groups that were internally short-circuited was determined. Furthermore, 10 electrode groups were inserted into a cylindrical case, and a 30 wt% potassium hydroxide aqueous solution was injected as an electrolyte solution and sealed with a sealing plate to obtain a cylindrical nickel-metal hydride storage battery having a theoretical capacity of 3000 mAh. This battery was charged and discharged at a current of 1 hour rate (1 It), and the average value of the discharge capacity and the representative value of the average discharge voltage (the value having the fifth largest value) were obtained. All these results are shown in (Table 1).

As is clear from (Table 1), in Examples 1 to 5, the depth of the maximum crack is reduced compared to Comparative Example 1, and as a result, the internal short-circuit occurrence rate is reduced. When it sees in detail, there exists a tendency which can reduce an internal short circuit incidence rate by suppression of a crack, so that the thickness of the metal rich layer 3 is large. Further, it can be seen that by periodically changing the position of the metal rich layer 3 in the thickness direction, the depth of the maximum crack is remarkably reduced and the internal short-circuit occurrence rate is drastically reduced. .

  Although the crack of the electrode of Comparative Example 2 was not observed, the incidence rate of internal short circuit was higher than that of each Example. Looking at the location where the internal short circuit occurred, the occurrence location is a portion where the three-dimensional porous metal body 1 is exposed, and the discontinuous metal skeleton of the metal rich layer 3 protrudes from the electrode surface by winding and breaks through the separator, The possibility of contact with the negative electrode is considered high.

  From the results of the discharge capacity and the discharge average voltage characteristics, it can be seen that the discharge characteristics of Examples 1 to 5 are improved with respect to Comparative Example 1. This is due to the presence or absence of the metal rich layer 3. If it sees in detail, there exists a tendency for a discharge characteristic to improve, so that the thickness of the metal rich layer 3 is large. Further, by periodically varying the metal rich layer 3 in the thickness direction, the discharge characteristics could be improved even when the metal rich layer 3 had the same thickness. These are considered to be caused by the fact that the current collecting property is improved by suppressing cracks.

  However, in the case of Example 5 in which the ratio of the thickness of the metal rich layer 3 to the thickness of the electrode is 3%, since the metal rich layer 3 is relatively thin, the above-described effect is slightly reduced. On the other hand, in Example 4 where this ratio is 20%, it can be seen that the depth of cracks and the occurrence rate of internal short-circuits have deteriorated. This is because the ratio of the thickness of the metal rich layer 3 is made too large while keeping the weight per unit area of the three-dimensional porous body 1 constant in order to maintain the battery capacity. It is presumed that the metal skeleton at this point became thinner by filling, causing a crack at the time of winding and inducing an internal short circuit. Therefore, the ratio of the thickness of the metal rich layer 3 to the thickness of the electrode is preferably 5 to 15%.

Since the secondary battery using the secondary battery electrode of the present invention has both high discharge characteristics and excellent short-circuit resistance, it is suitable for tough use applications such as an auxiliary power source for hybrid electric vehicles and a power source for electric tools. The availability is extremely high.

Schematic sectional view showing an electrode for a secondary battery of the first invention Schematic sectional view showing a conventional secondary battery electrode Schematic sectional view showing a secondary battery electrode of the third invention Schematic sectional view showing the first step in the method for manufacturing a secondary battery electrode of the fourth invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Three-dimensional metal porous body 2 Active material 3 Metal rich layer 4 Paste discharge nozzle 5 Paste 6 Electrode precursor

Claims (5)

An electrode for a secondary battery in which an active material is filled in a void of a three-dimensional metal porous body,
An electrode for a secondary battery, wherein a metal-rich layer having a metal density of the three-dimensional porous metal body larger than other portions is provided at a portion excluding a surface layer portion in the thickness direction. 2. The electrode for a secondary battery according to claim 1, wherein a ratio of the thickness of the metal rich layer to the thickness of the electrode is 5 to 15%. 2. The electrode for a secondary battery according to claim 1, wherein the position of the metal rich layer is periodically changed in the thickness direction of the electrode. A method of manufacturing an electrode for a secondary battery in which a paste mainly composed of an active material is filled in the voids while running a band-shaped three-dimensional metal porous body,
A first electrode precursor is produced by discharging the paste from a pair of paste discharge nozzles arranged on both surfaces of the three-dimensional metal porous body so that an unfilled portion remains inside the three-dimensional metal porous body. And the process of
A second step of drying the electrode precursor;
A third step of rolling the electrode precursor;
The manufacturing method of the electrode for secondary batteries characterized by including. In the first step, the discharge amount of one paste discharge nozzle and the other paste discharge nozzle is periodically changed while making the total amount of the paste discharged from the pair of paste discharge nozzles substantially constant. The manufacturing method of the electrode for secondary batteries of Claim 4 characterized by the above-mentioned.